Quality of service (QoS) mechanisms allocate transmission resources to different types or classes of data traffic so that certain traffic classes can be preferentially served over other classes. For example, in a network that supports multimedia services like video-on-demand, video conferencing, online brokerage, and electronic commerce, a QoS mechanism can prioritize time-sensitive multimedia data streams so that their packets are transmitted—over a communication medium or channel shared by two or more terminals or stations—with less delay and/or at a higher rate than packets of data streams less affected or unaffected by delay.
Local area networks (LANs) are increasingly used to transfer data, including multimedia data streams that have various QoS requirements. A multiple layer communication protocol “stack” such as the OSI reference model implements communication over the typical LAN. According to this model, the media access layer (MAC) is responsible for access control of a shared communication channel. A significant objective of any LAN is to allocate access to a shared communication channel as equitably as possible between the stations competing for it. A straightforward realization of this would be to implement, via the media access layer, a QoS scheme in which each of two time-sensitive streams of multimedia traffic—with each originating at a different station on the LAN—is assigned an identical level of transmission priority.
Consider, however, a scenario in which the first station has two distinct classes of traffic to transmit (e.g., from both a high priority class and a lower priority class) while the second station has only traffic from the lower priority class to transmit. At the first station, the higher priority class of traffic would be preferentially treated to the detriment of the lower priority class of traffic since both classes compete for the same transmission opportunity. The lack of any higher priority class of traffic to transmit at the second station, on the other hand, benefits the lower priority class of traffic insofar as there is no need to yield a transmission opportunity to a higher priority data message. As such, a need arises for a system and method of ordering data messages—prior to their transmission over a shared communication channel—such that traffic of equal priority is handled in a fair and equitable manner by all stations contending for access to the shared communication channel.